Paroxysmal nocturnal hemoglobinuria (PNH), also known as Marchiafava-Micheli syndrome, is a rare, acquired, life-threatening disease of the blood characterized by destruction of erythrocytes by the complement system.
Normally, blood cells are protected from complement destruction by proteins including decay-accelerating factor (DAF/CD55), which disrupts formation of C3-convertase, and protectin (CD59/MIRL/MAC-IP), which blocks formation of the membrane attack complex by preventing C9 from incorporating into the complex. These proteins, CD55 and CD59, are anchored to the cell membrane by glycosyl phosphatidylinositol (GPI), a glycolipid that is attached to the C-terminus of certain proteins during posttranslational modification. GPI comprises a phosphoethanolamine linker that attaches to the C-terminal of the protein, a glycan core, and a phospholipid moiety with hydrophobic lipid tails that anchor the protein-GPI structure to the cell membrane.
PNH patients have defects in GPI synthesis, so that the proteins, particularly CD55 and CD59, that protect the cell from destruction by complement are not properly anchored to the cell membrane. In the most common case, there is a somatic mutation in the gene for phosphatidylinositol N-acetylglucosaminyltransferase subunit A (PIGA), which is required for synthesis of N-acetylglucosaminyl phosphatidylinositol (GlcNAc-PI), which is the first intermediate in the biosynthetic pathway of GPI anchor. The PIGA gene is located on the X chromosome, which means that only one active copy of the gene for PIGA is present in each cell (males have only one X chromosome; in females the second X chromosome is silenced through X-inactivation). Mutation of the PIGA gene thus can lead to the absence of functional GPI anchors. When this mutation occurs in a hematopoietic stem cell (HSC), all of the subsequent progeny of this cell will have the same mutation. PNH may arise on its own (“primary PNH”) or in the context of other bone marrow disorders such as aplastic anemia (“secondary PNH”). Because the mutation does not necessarily affect all progeny lines of erythrocytes, patients may have varying degrees of the disease, with only some, or most, or substantially all of the erythrocytes failing to present CD55 and CD59.
PNH can be diagnosed by measuring levels of CD55 and CD59 presentation on erythrocytes or by measuring GPI. In one method, flow cytometry for CD55 and CD59 on white and red blood cells is used to categorize erythrocytes as type I, II, or III PNH cells, wherein type I cells have normal levels of CD55 and CD59; type II have reduced levels; and type III have absent levels. In another method, fluorescein-labeled proaerolysin (FLAER), which binds selectively to the GPI, is used to measure GPI levels on erythrocytes.
Symptoms of PNH include red or dark urine due to the presence of hemoglobin and hemosiderin from the breakdown of red blood cells, as well as symptoms of anemia, such as tiredness, shortness of breath, and palpitations. Patients may have abdominal pain, difficulty swallowing and pain during swallowing, esophageal spasm, erectile dysfunction, headache, hypertension, and/or pulmonary hypertension. It is believed that these symptoms are caused by hemoglobin released during hemolysis, which binds circulating nitric oxide, thereby inhibiting relaxation of vascular smooth muscle. Blood clots may develop in common sites (deep vein thrombosis of the leg and resultant pulmonary embolism when these clots break off and enter the lungs), as well as the hepatic vein (causing Budd-Chiari syndrome), the portal vein of the liver (causing portal vein thrombosis), the superior or inferior mesenteric vein (causing mesenteric ischemia), veins of the skin, and in the brain (stroke).
Allogeneic bone marrow transplantation, to replace the defective HSCs with healthy HCSs, has significant risks, such as graft-vs-host disease or failure of the graft, and suitable donors may not be available. The monoclonal antibody eculizumab, which blocks terminal complement activation, reduces the need for blood transfusions and improves quality of life in PNH patients, but does not reduce overall mortality or the incidence of clots. See, Marti-Carvajal, A J, et al. “Eculizumab for treating patients with paroxysmal nocturnal hemoglobinuria,” The Cochrane database of systematic reviews 10: CD010340 (30 Oct. 2014). Currently, treatment of PNH is most often symptomatic, with blood transfusions and supplementation with folic acid or iron for the anemia, and anticoagulants for the clotting. Transfusions, in addition to reducing the severity of the anemia, may suppress production of the defective PNH erythrocytes, thereby reducing damage to the small blood vessels by accumulation of damaged cells and reducing symptoms caused by hemoglobin released during hemolysis. PDE5 inhibitors may be used to mitigate the effect of hemoglobin binding to nitric oxide. Corticosteroids such as prednisolone, or other immunosuppressive drugs are sometimes used in an effort to suppress the complement-mediated destruction of the erythrocytes.
New approaches to the treatment and management of PNH are needed.
Deer antler is a traditional Asian medicine, prepared by drying uncornified antler of deer. Deer antler has been acclaimed to have various medical effects, such as growth- and development-promoting effects, promoting hematopoietic function, treating nervous breakdown, benefiting cardiac insufficiency, and improving the function of five viscera and six entrails, as described in the Dong-eui Bogam, a Korean medical book first published in 1613. It has been reported that certain components of deer antler, including rac-1-palmitoyl-2-linoleoyl-3-acetylglycerol (PLAG) obtained from chloroform extracts of the deer antler, have growth-stimulating activities of hematopoietic stem cells and megakaryocytes (WO 99/26640). It is also reported that monoacetyldiacylglycerol derivatives which are active components of the deer antlers are effective in treating autoimmune diseases, sepsis, cancers such as bile duct cancer, kidney cancer or malignant melanoma, and so on (WO 2005/112912). Use of certain monoacetyldiacylglycerol derivatives for treatment of leukopenia and/or thrombocytopenia is described, e.g., in International Application No. PCT/US2015/031204, the contents of which are incorporated herein by reference.